The present invention relates to an engine of an outboard motor having an improved structure of a fuel pump arrangement for making compact the engine of the outboard motor.
In known engines of outboard motors, some of the engines are provided with a mechanical fuel pump (mechanically operative fuel pump) which is driven by a reciprocal motion of a plunger. The plunger is usually driven by a pump driving cam mounted on a cam shaft constituting a valve moving mechanism of the engine.
As one example of such prior art, the Japanese Patent Laid-open Publication No. HEI 8-93585 shows a fuel pump arrangement, in which a fuel pump is arranged above a cylinder head at a portion near an intermediate portion, in the longitudinal direction, of the cam shaft and the pump driving cam and the plunger are coupled by means of a rod-shaped driving member.
However, in the structure of the above prior art publication, it is necessary to locate a support member for supporting the driving member in the cylinder head, which results in that the cylinder head is made large in size and complicated in shape, thus being inconvenient.
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide an engine of an outboard motor comprising:
an engine casing;
a plurality of cylinders arranged vertically in the engine casing;
a cylinder head to which the cylinders are mounted and in which a valve moving mechanism comprising a cam shaft is housed;
a cylinder block disposed in the engine casing;
a crank case joined to the cylinder block;
a crank shaft disposed vertically at the joining portion between the crank case and the cylinder block;
a fuel pump provided with a plunger and sucking a fuel from a fuel tank through a reciprocal motion of the plunger;
a plurality of bearing bosses each disposed between adjacent cylinders, the bearing bosses supporting the cam shaft;
a pump driving cam mounted on the cam shaft and adapted to drive the fuel pump; and
a driving mechanism disposed between the adjacent cylinders, supported by the bearing bosses and adapted to transfer a rotational motion of the pump driving cam to the plunger so as to perform a reciprocal motion thereof.
In a preferred embodiment, the bearing bosses are integrally formed with the cylinder head. Each of the bosses is composed of a cylindrical member having an inner hollow portion. The cam shaft is provided with a plurality of bearing journals each disposed between the adjacent cylinders, the pump driving cam is disposed adjacent the bearing journal, and the bearing journal and the pump driving cam are accommodated and supported in the bearing boss.
The pump driving cam and the driving mechanism are disposed in the vicinity of a vertically intermediate portion of the engine in an operative state thereof.
According to the present invention of the structures mentioned above, the pump driving cam for driving the fuel pump is disposed between the cam rows of the adjoining cylinders (first and second cylinders in the described embodiment) and the pump rod for the fuel pump is supported by the one of the bearing boss in which the pump driving cam is housed. Accordingly, it is not necessary to specifically locate any support member for the driving member which has been required in the conventional structure. As a result, it is also not necessary to set a space in the cylinder head for locating the support member, thus making compact the cylinder head and making simple the shape thereof, which contributes to the manufacturing cost reduction.
Furthermore, the bearing bosses for accommodating the bearing journals are also formed, as well as the pump driving cam, to the cylinder head, so that the number of the constructional elements or members can be eliminated.
Still furthermore, since the pump driving cam is disposed in adjacent to the bearing journal and is accommodated in the bearing boss together with the bearing journal, the lubrication oil lubricating the sliding surface between the bearing journal and the bearing boss can also lubricate the sliding surface between the pump driving cam and the pump rod.
Still furthermore, the pump driving cam is disposed between the cam rows of the adjoining cylinders, so that the fuel pump can be arranged to a portion near the vertically intermediate portion of the engine, i.e. cylinder head. As a result, the height difference in locations between the fuel pump and the intake device such as carburetor is reduced (there is less difference in location levels therebetween), so that the fuel pump having relatively low pumping ability can be utilized.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions mentioned with reference to the accompanying drawings.